Elevator systems generally include an elevator car suspended by a rope (as wire cables are called within the elevator industry) or coated steel belt system. The car is guided along guide rails within an elevator hoistway so that relatively little lateral motion is imparted to the car during use. Passenger elevators are required to have a braking system to halt the elevator car in an overspeed event. Such a braking system is commonly activated by an actuation device known as a governor. The governor detects excessive speed of the car and actuates an emergency stop device.
The governor system typically consists of sheaves at the top and bottom of the hoistway with a governor rope reeved in an endless loop over both sheaves. A part of the governor rope is connected to a safety link that is mounted on the elevator car frame. As the car ascends and descends, the governor rope travels with it, rotating the sheaves. One of the sheaves has a centrifugal governor mounted in it, so that when the sheaves rotate too fast, paired flyweights or flyballs rotating on a spindle are accelerated outward by centrifugal force, where they trip an overspeed switch, thus cutting power to the elevator drive motor. If further overspeed occurs, a clamping device is actuated that clamps onto the governor rope to activate the braking safeties, bringing the elevator car to a safe albeit abrupt stop.
More modern systems omit the stationary governor pulley and rope combination by fitting each elevator car with its own governor, such as that disclosed in U.S. Pat. No. 5,377,786 (Nakagawa) or in U.S. patent application Ser. No. 09/428,023 filed on Oct. 27, 1999 and entitled ROTARY ACTUATED OVERSPEED SAFETY DEVICE, incorporated herein by reference.